Pin constraints conflict with routing blockages or PG shapes. Who owns the fix?
From PDVerse PnR Interview Handbook · pdVerse Mentor Guide
Short Answer
Identify whether package/interface intent, block pin constraints, routing blockage, or PG reservation is authoritative, then negotiate a geometry that preserves the required function.
Technical Explanation
Both constraints may be valid separately but impossible together. Use pin checks, reported layer/side/offset, local blockages, and planned PG corridors. Keep differential, clock, and supply needs explicit.
Formula Or Decision Rule
Decision rule: the final pin has legal access and the blockage/PG purpose remains satisfied.
What To Check
• Warning sign: One team deletes the other team’s constraint locally. • Inspect: choose one affected region, macro, row, pin, path, or net and trace the physical cause. • Correct: Return evidence to the interface, floorplan, or power owner, agree on the change, and rerun both checks.
Command Checks & Actions
• check_pin_placement -blocked_only true: checks pin-placement legality and access-related conditions
• report_pin_placement -pins <pins> -format {layer side offset}: reports pin layer, side, and offset
• report_congestion -mode hot_spot: reports routing demand, capacity, overflow, or hot spots
Run only the commands needed for this question. Save the report with the floorplan version and analysis context.Healthy, Suspicious & Hard-stop Results
• Healthy: Identify whether package/interface intent, block pin constraints, routing blockage, or PG reservation is authoritative, then negotiate a geometry that preserves the required function. • Suspicious: One team deletes the other team’s constraint locally. • Hard stop: required legality or physical feasibility is missing or unexplained. Return evidence to the interface, floorplan, or power owner, agree on the change, and rerun both checks.
Common Mistake
Do not hide the symptom with an arbitrary utilisation, halo, channel, blockage, pin move, or die-size change. One team deletes the other team’s constraint locally.
What The Interviewer Is Testing
The interviewer is testing whether you can connect “Pin constraints conflict with routing blockages or PG shapes. Who owns the fix?” to measurable physical evidence and an owned correction.
Follow-up Question & Model Response
Follow-up probe: What would make you change your decision? Model response: “I would change it if the same controlled rerun shows that one team deletes the other team’s constraint locally. I would use the named objects and reports to decide whether to iterate, waive, or return the issue.”
Practical Example
Symptom: One team deletes the other team’s constraint locally. Corrective path: Return evidence to the interface, floorplan, or power owner, agree on the change, and rerun both checks.
Continue practising